Conventionally, a content data such as audio data, image data, moving-picture data, game program, computer program, etc. is recorded in a recording medium such as an optical disc, tape cassette or the like for commercial distribution, and a user having purchased the recording medium can permanently reproduce the content data from the recording medium.
For example, in the field of commercial distribution of an audio data via a network such as the Internet, the audio data is encrypted for distribution from a server to each terminal unit. The user wanting to reproduce the audio data at his own terminal unit will buy an encryption key to decrypt the encrypted audio data, that is, he or she will download the encryption key by paying a due compensation or money for the encryption key and store it in his or her storage unit such as a hard disc, nonvolatile memory or the like, while the audio data serving side will be able to receive a compensation for the audio data. In this case, the user will have to decrypt the encrypted audio data downloaded using the encryption key stored in his storage unit in order to permanently enjoy the audio data.
However, many such users own a plurality of audio data players such as a personal computer, stationary player, on-vehicle player, portable player and the like. With the above-mentioned copyright management system, however, the users going to enjoy such an audio data can only reproduce the encrypted audio data by his own player in which an encryption key for the audio data is stored.
To reproduce an encrypted audio data by a player owned by a user going to enjoy the audio data and which has not stored therein any encryption key for the audio data, it has been proposed to connect a player the user is going to use to a one having the encryption key stored therein via a network and thus use the encryption key in common between the player the user is going to use and a one having the encryption key stored therein. Besides, it has also been proposed to design a removable storage unit having the encryption key stored therein and for the user of a player to connect the removable storage unit to his own player. In any case, the user has to build the network or carry on the storage unit having the encryption key stored therein, which will make it complicated or troublesome for the user to enjoy such an audio data.
To solve the above problems, there is currently available a system by which only a player having downloaded an encrypted audio data can decrypt the audio data with an encryption key for reproduction of the audio data. However, it is desirable that any player owned by a user having purchased an audio data can always reproduce the audio data only if the reproduction is limited to a range of private use by the user.